Symantec Management Agent (also known as Altiris Agent) is registered with a Task Server but it does not receive new tasks. 

Entry from the agent log:

Operation 'Direct: Head' failed. 
Url: HTTPS://<servername>.example.com:443/Altiris/ClientTaskServer/Register.aspx?lastResort=true&resTypeGuid=%7B493435F7-3B17-4C4C-B07F-C23E7AB7781F%7D&sysType=Win64&version=8.7.2337&resourceGuid=MACHINEGUIDHERE&crc=0008000700000921 
Connection path: 1 - Direct: [IP address Here] -> <servername>.example.com [IP address Here] 
Connection id: 917.6536 
Communication profile id: {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx} 
Throttling: 0 0 0 
Connecton stage: Server connect 
Error type: HTTP error 
Error code: HTTP status 403: The client does not have sufficient access rights (0x8FA10193) 
Error note: 403 Forbidden 
Server SSL connection info: 
   Server certificate: 
      Serial number: xxxxxxxx 
      Thumbprint: xxxxxxxx 
   Client certificate: 
      Serial number: xxxxxxxx 
      Thumbprint: xxxxxxxx 
   Cryptographic protocol: TLS 1.2 
   Cipher suite: TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 
   Cipher algorithm: AES 
   Cipher key length: 256 
   Hash algorithm:  
   Hash length: 0 
   Key exchange algorithm: ECDH 
   Key length: 384 
Client SSL attributes for server connection: 
   Client certificate: 
      Serial number: xxxxxxxxx 
      Thumbprint: xxxxxxxxx 
   Cryptographic protocol: TLS 1.0, 1.1, 1.2
-----------------------------------------------------------------------------------------------------
Date: 11/13/2023 10:45:34 AM, Tick Count: 440299359 (5.02:18:19.3590000), Size: 1.79 KB
Process: AeXNSAgent.exe (6536), Thread ID: 13296, Module: AeXNetComms.dll
Priority: 1, Source: NetworkOperation

ITMS 8.x

The IIS setting is changed and server is accepting client's certificate

Try the following:

1. Remote to the Site Server mentioned on the agent log entry
2. Open IIS manager> Default Websites> Altiris > Altiris Client Task Server
3. Open the SSL Settings in the middle pane
4. Make sure settings under Client certificate are set to "Ignore", and "Require SSL" is not selected.
5. Restart IIS service: run from the command prompt as Administrator the following command:
   iisreset